Ukrainian helicopters blasted a gasoline storage tank in western Russia, causing a massive fire, according to the regional governor, in the first confirmed air strike by Kiev on Russian soil.

The declaration occurred on the 37th day of Russia’s military campaign in Ukraine, which has resulted in thousands of deaths and over 10 million displaced people in Europe’s biggest refugee crisis since World War II.

The bombing near Belgorod, Russia, was the first time Russia has acknowledged a Ukrainian airstrike on its territory since the conflict began.

“A fire broke out at the petrol station as a result of an air attack carried out by two Ukrainian army helicopters that invaded Russian territory at a low height,” Belgorod area governor Vyacheslav Gladkov posted on the messaging app Telegram.

According to another post, two employees at the storage facility were hurt in the incident.

The massive incident, which began at 6 a.m. (0300 GMT), was being fought by 170 firemen, according to the emergency ministry.

According to a video posted by the ministry, a big fire was blazing, with black and white smoke rising overhead.

The facility’s owner, the Russian oil company Rosneft, claimed it had evacuated its employees.